LEED/Auger studies with Ir(110) revealed that the clean surface is reconstructed to a 1X2-structure, whereas the normal 1 X 1-structure can be stabilized by small amounts of carbon impurities. Carbon monoxide adsorbs with a mean heat of adsorption of 37 kcal/mole and forms a 2X1-structure without affecting the substrate “extra” diffraction spots. Adsorbed oxygen forms 2X2-and c2X2-structures, whereby the diffraction features of the 1 X 2-structure disappear indicating that oxygen atoms cause place exchange process of the Ir surface atoms which is not the case with adsorbed CO. Carbon monoxide tends to dissociate at elevated temperatures. The catalytic oxidation of CO proceeds in a manner similar to that found with Pd and Pt surfaces. © 1973, Walter de Gruyter. All rights reserved.